freedreno: add fd_pipe refcounting

In mesa/gallium, a pipe_fence can outlive the pipe_context it was created from. But to wait on the fence we need to know the submit-queue (ie. the fd_pipe).

The most straightforward way to fix this is to add reference counting to the fd_pipe and let the fence hold a reference to the pipe (rather than hanging on to the context, which might have been destroyed before the fence).